Classic mechanical pushbuttons generally comprise a transverse head in relation to the centrepart of a watch case, of which a lower end comes to rest against a movable or plastically deformable element such as a blade of an operating device, for example. When the pushbutton is pressed in, the end of this transverse head causes the movable element to move, and this comes into abutment to activate a mechanical or electronic function. Moreover, the coming into abutment enables the user to have a mechanical confirmation of the actual activation of the desired function by the pushbutton. However, this solution poses problems of sealing in relation to the interior of the case. In fact, the seal is only guaranteed when resting, but never completely upon activation under water because of the friction exerted on the joints, typically the O rings, past a relatively shallow depth. Moreover, compression of the joints greatly increases the force threshold to be applied to press in the pushbutton, which makes use relatively inconvenient.
Capacitive operating devices are, moreover, known that are used as proximity switches, for example, for touch screens or digital photographic devices. This type of device can certainly allow physical isolation of the interior of a case in theory, since it does not require a transverse element similar to the usual solution for watch pushbuttons, but it still has the disadvantage of automatically detecting a variation in electrical capacitance on contact with water, which makes it unsuitable for use when immersed where it would no longer be possible to dissociate the actual activation by the user from that caused merely by contact with water. Moreover, the adaptation of such a device to the dimensions of a wristwatch poses substantial problems in terms of detection thresholds, since the capacitance depends, amongst other factors, on a relation between the surface of the armatures and their spacing, which becomes difficult to manage when the contact surfaces are considerably reduced and, above all, when the minimum spacing between the armatures is relatively large, which is the case when the conductive elements of the capacitance used for the detection are arranged on either side of a hermetic insulating plate.
Moreover, resistive operating devices are also known, for example, for computer keyboards, wherein pressing a key to abut against a conductive surface allows an electric circuit to be closed and an electronic function to be activated. A pushbutton is also known from document U.S. Pat. No. 2,262,777 that forms a resistive electric switch intended to be integrated into an aircraft joystick, for example. Pressure on the pushbutton allows a capsule to be deformed, under which a movable conductive element is riveted that can be brought into contact with a fixed conductive element arranged in the body of the pushbutton. However, such devices are likewise unsuitable for use under water because of their lack of seal, nor can they be replicated for a wristwatch because of the high consumption of electric power necessary for permanent charging of the detection circuit, which would have a very negative impact on the service life of the battery.
In the field of watchmaking, a pushbutton coupled to an electrical switch is known from document FR 2327623 that comprises star-shaped conductive elastic elements, the deformation of which allows a circuit to be closed and which in parallel exert a restoring force to return to their resting position. However, the seal of the pushbutton is only assured by O ring-type seals in accordance with classic mechanical pushbuttons with the same disadvantages of reliability in terms of hermetic seal for activation when immersed and of the minimum force threshold to be applied because of the deformation of the joint.
There is therefore a need for a sealed pushbutton for wristwatches without the known limitations.